Preparation And Characterization Studies Of Low Melting Point Polyamide

Low melting point polyamide (LMPA) is a class of modified products with lower meltingpoint than conventional polyamide. It has prominent characteristics such as controlled meltingpoint, narrow melting range and excellent adhesion properties, and has been used for hot-meltadhesive, fiber spinning and photosensitive adhesive. Among these applications, there are morereports on nylon hot-melt adhesive and the products have achieved the industrialization level. Inrecent years, its demand is growing with the expansion of LMPA fiber’s applications, however,currently, LMPA fiber mainly rely on imports due to some problems associated with the inherentquality and spinning technology of LMPA fiber. Using LMPA as fiber, the certain requirements ofthe melting point, suitable crystallinity and good spinnability were needed to meet spinningrequirements. By systematic study of selecting monomer, determining component ratio,controlling synthesis process and characterization, this research provides a theoretical referencefor the industrialization of fiber grade LMPA.Using dodecanedioic acid, decamethylene diamine, decanedioic acid, hexamethylenediamine and caprolactam as raw materials and Irganox1076as antioxidant, low melting pointnylons with different proportions of diamines were prepared through the direct meltpolymerization in3-litre high pressure autoclave. Fourier transform infrared spectrometer (FTIR)spectra of obtained samples showed the typical characteristic peaks of nylon.1H-NMR spectra ofobtained samples showed almost all of monomers have copolymerized.Differential scanning calorimeter (DSC) tests indicated that the melting point of polymersdecreased significantly when the ratio of variable monomers was close to1:1.As the ratio ofcaprolactam, hexamethylene diamine, decamethylene diamine, decanedioic acid anddodecanedioic acid was1.33:1:1:1:1, the melting point of copolyamide was112.70oC. The resultsof the boiling water extraction demonstrated that the contents of both monomer and the oligomerin the LMPA were less than0.65%when the mole percentage of caprolactam was40%.Thermogravimetric analysis (TGA) evidenced that all of LMPA have excellent thermostabilitywhich was improved with the increase of long carbon chain monomers content. Water absorption rate of the samples reduced with the increase of long carbon chain monomers content according tothe water absorption tests.The non-isothermal crystallinity has been tested by differential scanning calorimeter (DSC)for LMPA. Result showed that with the increase of heating rate, the cold crystallization peaktemperature increased, crystallization temperature interval broadened and crystallization enthalpyincreased firstly, and then decreased. Crystallization enthalpy decreased when the ratio of twokinds of diamines was close to1:1. Crystallization peak temperature decreased with the increase ofdecamethylene diamine percentage. Avrami equation and Mo approach have been adopted tostudy this processes. Under different heating rates, the calculated Avrami index n of same LMPAwere close, which indicated crystal growth pattern of same LMPA, in non-isothermal terms, maynot be effected by heating rate. With the increase of heating rate, crystallizing rate of LMPAshowed an increasing trend firstly, and then a stability. Crystallization rate decreased when theratio of two kinds of diamines was close to1:1.The rheological properties of five kinds of LMPA which were similar in relative viscositywere investigated with a capillary rheometer. The results showed that LMPA exhibited apseudoplastic fluid flow feature. Apparent viscosity of LMPA decreased with the decrease ofmelting point. Under the similar melting point and relative viscosity, the apparent viscosity ofLMPA with higher percentage of decamethylene diamine was somewhat lower than LMPA withlower percentage of decamethylene diamine. Flow activation energy of LMPA decreased with theincrease of the shear rate and decamethylene diamine percentage. Non-newtonian index nincreased with the increase of temperature and decamethylene diamine percentage. It is importantto select a right temperature for LMPA with different melting point and ratio during processing.